Evidence for simultaneous production of $J\mathrm{/}\psi$ and $\mathrm{{\rm Y}}$ mesons

We report evidence for the simultaneous production of $J\mathrm{/}\psi$ and $\mathrm{{\rm Y}}$ mesons in 8.1 fb${}^{-1}$ of data collected at $\sqrt{s}=$1.96 TeV by the D0 experiment at the Fermilab $p\bar{p}$ Tevatron Collider. Events with these characteristics are expected to be produced predominantly by gluon-gluon interactions. In this analysis, we extract the effective cross section characterizing the initial parton spatial distribution, $\sigma_{eff}=2.2\pm 0.7\mbox{(stat)} \pm 0.9 \mbox{(syst)} ~\mbox{mb}$.